Tight-holding bolt and nut



H. L; DARDE LET' TIGHT HOLDING BOLT AND NUT Filed May 1925 2Sheets-Sheet 1 Jan. 24, 1928.

Jan. 24, 1928.

I 1,657,244 H. L. DARDELET I TIGHT HOLDING BOLT AND NU! Filed May 19,1925 2 Sheets-Sheet 2 Pasha-a Jan. 24, 1928. 1,557,244 UNlTED STATESPATENT OFFICE.

HUGUES LOU IS DARDELET, OF NANTES, FRANCE, ASSIGNOR T SOCIETE FRANCAISEDE FILETAGE INDESSERRAZBLE D. D. G., OF PARIS, FRANCE.

TIGHT-HOLDING BOLT AND NUT.

Application filed Kay 19, 1925, Serial No. 31,392, and in FranceSeptember 5, 1924.

My invention has for certain of its obmerit between the parts and atleast one of jects to provide an improved screw coupling which makes anangle with the axial line of for two members such, for example, as abolt the thread on which it is formed, and whereand nut, which willwithstand great strain in the male and female threads have opposed inthe direction of uncoupling; to provide face portions for positivelylimiting the ex- 00 a simple and efficient screw coupling wheretent-ofcrosswise movement between the firstin the coacting threads are soformed as to mentioned face portions of the two threads. permit readyconnection and disconnection Furthermore, the invention comprises proofthe parts by relative turning movement, riding a tight-holding screwthread conneceffected by a wrench or other suitable tool, tion for twoparts, such as a bolt andnut, 65 but to prevent accidental unscrewing;and wherein the coacting threads are formed to to provide atight-holding threaded connecpermit a substantial or appreciablerelative tion for two members such as a bolt and nut, displacementbetween the threads crosswise so formed that liability of rupture duringof the threads, i. e. axially of the screw or after connection of theparts is reduced to thread connection, in the direction of discon- 7 aminimum, and that the members'may be nection toetfect jamming betweencoacting repeatedly connected and disconnected with-, helicoidalreaction face portions of the out materially affecting the efficiency ofthe threads,.and are also so formed as to posithreaded connection, vtively limit the extent of such relative dis- My inventionalso'comprises providing a placement. The invention further com:fastening means comprising a nut and a bolt prises providing atight-holding screw threaded for connection with each other, threadconnection wherein the coacting wherein the nut and bolt threads are ofthreads have coacting helicoidal reaction face equal and constant pitchand each has a uniportions, making an angle with the axial line formcross-sectional contour at all points in of the threads less than theangle of fricthe length thereof, and wherein the crosstion, and coactinghelicoidal reaction face sectional thread contours are such as toperportions making an angle with the axial line mit easy unscrewing ofthe nut and to proof the threads greater than the angle" of ride opposedinitially acting thread surfaces friction, the pitch of the threads andthe for advancing the nut to the work and for relative widths of thecoacting face poreffecting tight holding of one thread to the tionsmaking the lesser angle being corother upon screwing of the nut againstthe related to permit firm jamming ofsaid latwork and opposed finallyacting thread faces ter face portions on each other before the foreffecting tight screwing of the nut faces making. the greater angle comeinto 35 against the work. engagement. o My invention also includes theprovision Preferably, also, the invention comprises of a screw threadconnection between two a tight-holding screw thread connection partswherein the interfitting threads are wherein complementary threads ofequal of equal and constant pitch and of such pitch and depth are soformed as to ]am 40 cross-sectional contour as to allow axial play uponeach other upon relative axial displacewithin fixed limits and effecttight holding ment of the connected threads in one direcbetween saidparts upon taking up of the tion and so constructed as-to positivelylimit axial thread play in one direction-and free the degree ofrstrainbrought upon the parts relative turning movement between the partsby'the jamming and offer great resistance 45 upon taking up of the axialthread play in to direct axial stresses after amming of the the oppositedirection, and wherein the threads on each other. The invention alsothread contours are such as to offer great recomprises providing ascrew-thread on a sistance to axial stresses. Y threaded member whichthread has a reac- My invention also includes providing a tion faceformed with a jamming portion tight-holding thread connection for twoand a jamming movement limiting portion,

members wherein a male thread on one memand preferably has a reactionface formed her and a female thread on the other memwith two helicoidalface portions making an berhave opposed face portions of different angleto the axial line of the thread less widths adapted to be jammed oneacross the than the angle of friction, and an interme-- 65 other whilein engagement by axial movediate helicoidal face portion making an angleto the axial line of the thread greater than the angle of friction, thetwo face p01- .tions making the lesser angle differing in width.

The inventive idea may receive a variety of mechanical expressions, oneof which, for the purpose of illustrating the invention, is shown inFigs. 2, 3, 4, and 5 of the accompanying drawings, but it is to beexpressly understood that said drawings are for the purpose ofillustration only and are not designed to define the limits of theinvention, reference being had to the appended claims for -this purpose.

In said drawings Fig. 1 is a diagramn'latic partially Sectional view ofa known type of bolt and nut;

Fig. 2 is a view, partly in section and partly in side elevation, of anut and bolt made in accordance with the present invention;

Fig. 3 is an enlarged sectional detail view of the nut and boltillustrated in Fig. 2, showing the jamming faces and thejamming-action-limiting faces disengaged;

Fig. 4 is a View similar to Fig. 3, showing the jamming faces of the nutand bolt threads in engagement; and i Fig. 5 is a view similar to Fig. 4showing the jamming faces and the jamming-actionlimiting abutment facesin engagement.

As a general rule, the threads of bolts and nuts and other connectedscrew-threaded parts are of regular triangular, rectangular. or othersymmetrical form in cross-section the two side faces of the threadsmaking equal angles with the axial line of the thread.

In the case of the known type of nut shown in Fig. 1, the angles or. and,8 which form the two sides of the outline of the thread relatively tothe center line AB are equal.

The present invention provides an improved tight-holding bolt and nutarrangement which is characterized by the fact that the surface of eachthread subject to pressure during the screwing of the nut has a smallerinclination than the opposed face of the thread, i. e. as shown in Figs.2 and 4, in which a is the nut, 15 the bolt and the direction of thereaction upon the nut when it is screwed, is to the right, the device ischaracterized by the fact that the angle B is much smaller than theangle a which latter may be 90.

Calculation shows that this arrangement will comply with the necessaryconditions for the tight-holding, which may be practically setforth asfollows.

A nut is said to be tight-holding when the minimum moment (relative tothe axis) of the friction effort holding the nut to the bolt is greaterthan the maximum moment (relative to the axis) of the friction effortholding the nut to the bolted pieces. Herein the nut is more firmly heldupon the bolt than upon the said pieces 0, and during any jarring ormovement of the pieces, the said nut will be displaced relatively to thesaid pieces and not relatively to the bolt, so that the bolt and nutwill not come apart.

It is an easy matter to make calculationswith reference to the pitch,the diameter of the bolt head or of the nut and of the frictioncoefficient. of the metals in contact-of the value to be assigned to theangle 1 whereby the nut will hold fast under all accidentalcircumstances. The nut may however be removed by the use of a wrench, inthe known manner.

lVhen the pieces to be held together by the bolt and nut are notrequired to be clamped together with any great effort by screwing thenut, there may be assigned to the angle ,8 a value which is smaller thanwhat is otherwise required for ti ht holding, and such that uponscrewing the nut into place it will afterwards remain jammed upon thebolt even should the pieces be subject to a certain wear; herein the nutis held to the bolt in a manner which may be compared with that of ahoop which has been put on in the hot state.

(alculation will show the proper proportions between the diameter of thebolt, the pitch, the depth of the threads, and the friction coeilicientof the metals in contact, whereby the said jamming 0r gripping ac tionmay he obtained. Practically the out will be held fast on the bolt whenthe tangent of the angle ,8 becomes smaller than the frictioncoeflicient of the metals in contact. When the nut is thus jammed uponthe bolt, the pieces of work a may be subject to a certain wear withoutany loosening of the nut. But in spite of these conditions the nut maybe removed with a wrench by the use of an efi'ort which need not begreater than what was employed for screwing the nut. It will beapparent, however, that, where the pieces to be held together by thebolt and nut areto be clamped together with any great effort, the nutwill be liable to be either stripped from the bolt or burst inconstructions in which the aforesaid smaller value is assigned to theangle ,8. To obviate this drawback, while at the same time ohtaining theadvantage of the jamming of the nut on the bolt, I provide a thread asshown in Figs. 3, 4 and 5.

Referring to Figs. 3, 4 and 5, the part f, i of the thread as shown indot and dash lines is brought towards the centre line of the bolt by thedistance 7); the same is true for the threads of the nut, so thatinstead of the outline e f i j the thread will have the outline e g h ij The part of the thread 9 it that has been displaced in depth isgreater in width than the remainder i j. 1 effect a like displacementfor the thread of the nut, and each operative face thereof comprises twodisplaced parts Z m and n 0 of unequal width.

In these conditions, there will exist a space 1' between the faces m nof the nut and the faces h i of the bolt, so that when the nut is put onthe bolt, the threads of these two members will have the relativeposition shown in Fig. 3.

Upon tightening the nut, since the reaction is exercisedaccording to thearrow F, the .inclined faces I m g h on the one hand and n 0 i j on theother will be mutually slidable transversely or crosswise of each otherand will assume the position Fig. 4 wherein the nut will be jammed onthe bolt if the angle ,8 is small enough to comply with the aforesaidcondition for the jamming.

Should the effort urging the nut in the direction of the centre linebecome considerable, the threads will he additionally displacedcrosswise of each other and assume the position shown in Fig. 5 whereinthe faces at n and h 2' which are substantially perpendicular to thecentre line will now be in contact, thereby limiting the relativecrosswise sliding motion of the thread of the nut without positivelystopping the screwing up of the nut. It will he noted that thedisplacement of the reaction faces of the threads in de th willdetermine the size of the contact aces acting to prevent the nut frombeing torn off under abnormal stresses in the direction of the centreline, butnevertheless the nut will he tightly held Since the operativeface when the nutis screwed down is herein divided into two parts whichhave a certain spacing, it will he no longer neeessaryto incline bothparts, but only one of them; this is shown in the dotted lines in Fig.3. The outer face of the bolt thread is parallel to the centrelinc. Itis not essential that the faces f, g, m, n, 71,4, etc. of the bolt andnut should be exactly perpendicular to the centre line. and such, facesmay be tapered, as shown in the dotted lines Fig. 4, or rounded. asshown in the dotted lines in Fig. 5. or they may he beveled according toneeds. true for the faces g 71 Z m no, i j, which may be tapered inpart, employing for this portion any suitable outline. Obviously. theoutline with spaced parts as shown in Figs, 3,4.- antl 5 can be employedirrespective of the value of the angle [3 i. e, whether the nut isjammed upon the bolt or otherwise, supposing however that the conditionof tight holding is maintained.

It will be observed that the reaction faces of the two threads, i. e.the faces which coact to resist direct movement between the by reason ofthe small value of the angle The same is parts in the direction ofunscrewing are formed with coacting helicoidal abutment surfaces makinga considerable angle with the axial line of the thread; that thecoacting helicoidalfaces of the two threads opposed to the reactionfaces also make a considerable angle with the axial line of the threads;and that said coacting abutment surfaces and said coacting opposedthread faces positively limit the extent of direct axial play betweenthe threads and permit sufficient relative crosswise displacementbetween the threads lougitudinally of the axial line of the threads toallow helicoidal coacting jam surface portions of the reaction faces ofthe threads to shift into either jamming or free-turning relation witheach other.

It will be apparent from Fig. 5 that the coacting thread face portions mn, h i, posi tively limit the extent of the jamming action of the threadface portions 9 h, Z m, and i j, n 0 on each other, and also offer greatresistance to axial strain in the direction of disconnection of the twoSCI'GW-thlQitdOt'l parts, .and. as most clearly shown in Figs. 3 and 5,the threads are so formed as to permit suflicient direct axial playtherebetween to permit free. turning or effect a ti ght-holding jammingengagement between the threads.

Obviously, the thread which forms the subject-matter of'my saidinvention, is applicable not only to bolts but to screwthrcaded rods,metal screws, and like machine parts.

I claim:

1. In combination. a bolt and a nut in threaded engagement, the threadson the nut and bolt being of equal pitch and the pitch of the threadsbeing uniform from end to end, the cross-sectional contour of the twothreads being such as to permit axial play between the engaged threadsand to provide one pair of coacting thread faces for positively limitingaxial thread play in the direction of connection of the nut and bolt anda second pair of coacting thread faces having self-binding frictionsurface portions and surface portions for positively limiting axialthread play in the direction of disconnection of the nut and bolt.

2. A self-locking and tight-clamping fastening means comprising. incombination, a bolt and a nut provided with cooperating screw threadshaving side play therebetween, said two threads having the two sidesthereof which coact to advance the nut on the bolt into work-clampingposition formed with two co-acting hclicoidal initially-actingnut-advancing areas and two co-acting helicoidal finally-actiugnut-advancing areas, the initially-acting areas lying within the angleof friction transversely of the thread sides and being movabletransversely of each other into self-holding frictional engagement byreaction of the work during advance of the nut to fasteningposition, andthe finally-acting areas lying without the angle of frictiontransversely of the thread sides for finally advancing the nut intotight-clamping fastening position without increasing the transversemovement between the initially-acting areas and without increasing thereaction stresses imposed on the self-held iuitially-acting areas.

3. A tight-holding fastening means comprising a nut and a bolt threadedfor screwing together, the pitch of the nut thread and the pitch of thebolt thread each being constant and the contours of the threads beingsuch as to provide coacting nut and bolt thread portions forcible oneacross the other while in engagement by reaction stress incident toscrewing the nut onto the bolt into work-holding position, and toprovide coacting nut and bolt thread abutment surfaces for limitingpositively the extent of such relative crosswise movement between saidcoacting thread portions, one of said thread portions having the surfacethereof which is engaged by the other thread portion during suchcrosswise thread movement of zero curvature and making an angle with theaxial line of the bolt less than the angle of. friction.

4. A self-locking and tight-clamping fas tening means comprising, incombination, a bolt' and a nut provided with cooperating screw threadshaving side play therebetween, said two threads having the two sidesthereof which coact to advance the nut on the bolt into work-clampingposition formed with two co-acting helicoidal initially-actingnut-advancing surfaces of zero transverse curvature and two co-actinghelicoidal finally-acting nut-advancing surfaces of zero transversecurvature, the initially-acting surfaces making an angle with the axialline of the bolt less than the angle of friction and being movabletransversely of each other into self-holding frictional engagement byreaction of the work during advance of the nut to fastening position,and the finally-acting surfaces making an angle with the axial line ofthe bolt greater than the angle of friction and being movable by thereaction of the work into abutting engagement upon tight binding of theini-' tially-acting surfaces for finally advancing the nut intotight-clamping fastening position without increasing the transversemovement between the initially-acting surfaces and without increasingthe reaction stresses imposed on the self-held initially-actingsurfaces.

5. A separable threaded coupling for two parts, characterized by thefact that the two parts are provided with complemntary threads eachhaving its reaction face formed to provide two longitudinally extendingre action-taking surface portions of zero transverse curvature disposedat angles to the axial line of the coupling less than the angle offriction and separated by an intermediate longitudinally v extendingreaction-taking portion of zero transverse curvature disposed at anangle to the axial line of the coupling greater than the angle offriction.

6. A tight-holding screw coupling for two parts, characterized by thefact that the parts are provided respectively with internal and externalthreads of equal pitch, said two threads having their coacti'ng reactionfaces provided with coacting, longitudinally extending, friction-jammingS111? face portions of zero transverse curvature making an angletransversely thereof with the axial line of the coupling less than theangle of friction, said coacting friction-jamming reaction face portionsof the two threads being of different widths, said two threads havingtheir coacting reaction faces provided with coacting,reaction-motionlimiting surface portions of zero transverse curvaturemaking an angle transversely thereof with the axial line of the couplinggreater than the angle of friction, the pitch of the threads being socorrelated with the relative widths of said coacting jamming faceportions of the two threads as to permit shifting of the coactingjamming face portions into and out of jammed relation by relativedisplacement of the jamming portions axially of the threads.

7 tight-holding screw coupling as claimed in claim 6, wherein thereaction faces of the two threads are each provided with two jammingsurface portions of different widths located different distances fromthe axial line of the coupling at opposite sides of thereaction-motion-limitlng surface portion thereof, the narrow jammingsurface portion of each thread coacti-ng with the wide jamming surfaceportion of the complementary thread, the faces of the two threadsopposed to the reaction faces thereof being of-zero curvature and makingan angle transversely thereof with the axial line of the couplinggreater'than the angle of friction.

8. A tight-holding screw coupling for two members subject to strains inthe direction of uncoupling, comprising external and internal screwthreads on said members having, on the coacting faces thereof whichresist stra-ightline movement in the uncoupling direction, coacting jamortions adapted to jam frictionally on eac 1- other upon relativestraight-line displacement between the jam portions in uncouplingdirection and coacting non-jamming stop portions spaced apart when saidjam portions are in non-jamming relation and adapted to engage mutuallyand to limit positively the extent of displacement between said jamportions in the jamming direction.

9.1m combination, a male screw element, and a female screw elementengaged with the male screw element, the engaged male and female screwthreads on sald elements being of equal pitch and the cross-sectionalcontours of said threads being such as to provide coacting self-holdingfriction surfaces of zero curvature transversely of the threads makingan angle with the axial line of the threads within the angle offriction, and to provide abutment surfaces arranged to permit crosswisemovement between the sel holding surfaces into and out of selfholdingengagement and to limit positively the extent of such sidewise movementbetween the self-holding surfaces in both directions.

10. In combination, a pair of relatively rotatable members havingengaged threads, two opposed helicoidal side faces of the engagedthreads each having two helicoidal surface portions of different widthsand both of low slope relatively to the axial line of the threads, thenarrower surface portion of each thread side face being movable acrossthe wider surface portion of the other thread side face fromfree-turning relation into self-holding engagement, and said side facesof the two threads also having co-acting relatively abrupt surfaceportions engageable to prevent positively the generation of destructivestresses by crosswise movement of the first-mentioned surface portionsinto self-holding engagement, the two surface portions of each threadface having the low slope being arranged at opposite sides of the abruptsurface portion of the thread face different distances from the axialline of the thread.

11. In combination, a pair of members having interfitting male andfemale screw threads of equal pitch each having one face formed with twohelicoidal face portions, each of zero transverse curvature and making asmall angle with the axial line of the threads, and an intermediatehelicoidal face portion of-zero transverse curvature making a largeangle with the axial line of the threads, the face portions of the saidmale and female thread faces which make the large angle being opposed toeach other, the face portions of the said male and female thread faceswhich make the small angles being opposed to each other, and the opposedface portions of the said male and female thread faces making the smallangles being of different widths.

12. The combination of a member having an external screw thread, and asecond memher having an internal screw thread engaged with the thread onthe first member, the two threads being formed with coacting opposedhelicoidal surfaces so related as tolock the threads frictionallyagainst accidental relative turning. movement upon' a limited cross wisemovement between said surfaces of the threads in one direction, and alsobeing formed with coacting opposed helicoidal abutment surfacesengagcable only upon locking of the threads against accidental relativeturning movement and adapted to limit positively crosswise movementbetween the locking surfaces of the threads in the last-mentioned twoopposed surface portions 1 being co-related with the first-mentioned twoopposed surface portions for engagement thereof after tight-binding iselfected between the lirst-rnentioned two opposed surface portions andbefore the generation of destructive stresses by crosswise movement ofthe first-mentioned two surface portionsinto tight-binding engagement.

14. In combination, a pair of relatively rotatable members havinginterfitting male and female screw threads of equal pitch relativelydisplaceable crosswise of each other, one of said threads having ahelicoidal friction jam surface portion sloping slightly toward theaxial lineof the threads and crosswise of which the other thread isdisplaeeable while engaged therewith from free-turning relation intoself-locking rela-,

tion, and said two threads having coacting helicoidal abutment surfaceportions arranged for engagement only when said threads are displacedinto self-locking relation and disposed abruptly relatively to the axialline of the threads to limit positively relative crosswise displacementof the threads in the direction efiecting locking engagement between thethreads.

15. A nut, for use in a tight-holding bolt and nut fastening, having aninternal screw thread of constant pitch, said thread having the sidethereof which is subject to reaction stresses upon screwing of the nutona bolt formed with a helicoidal bolt-thread-engaging abutment surfaceportion disposed abruptly relatively to the axial line of the nut, andalso formed at each side of said abutment surface portion with ahelicoidal bolt-thread-engaging surface portion having a slight slopetoward the axial line of the nut.

16. A nut, for use in a tight-holding bolt and nut fastening, having aninternal Screw lot) thread of constant pitch, said thread having theside thereof which is subject to reaction stresses upon screwing of thenut upon a bolt formed to present a helicoidal boltthread-engagingsurface portion of sufiiciently slight slope toward the axial line ofthe nut to permit jamming thereof tightly upon a bolt thread by thereaction stresses, and also formed with a helicoidal boltthread-engagingsurface portion sufiicientlv abrupt relatively to the axial line of thebolt to limit positively the degree of the reaction stresses which canbe generated in screwing the nut on a bolt.

17. A bolt, for use in a tight-holding bolt and nut fastening, having ashank provided with an external screw thread of constant pitch having ahelicoidal reaction surface portion forming an abrupt shoulder facingaway from the nut-receiving end of the shank and also having at eachside of said surface portion a helicoidal reaction surface portionsloping slightly toward the axial line of the thread away from thenut-receiving and of the shank.

18. A bolt, for use in a tight-holding bolt and nut fastening, havingthe shank thereof formed with an external nut-holding screw thread ofconstant pitch provided with a helicoidal surface portion of suflicientlslight slope toward the axial line of the shank and so arranged as topermit jamming of a nut thread thereupon by reaction stresses due toscrewing the nut against the work, and also provided with a helicoidalsurface portion sufliciently abrupt relativelyto the axial line of theshank and so arranged as to limit positively the degree of the jamaction stresses which can Eel generated in screwing a nut upon the 19. Atight-holding screw element having a thread formed at one side thereoffrom end to end with three helicoidal reaction surface portions of equalpitch, the intermediate surface portion being dis osed abruptlytransversely thereof relative y to the axial line'of the thread and theother two surfaces being disposed transversely thereof at a slight angleto the axial line of the thread.

20. A tight-holding screw element having a thread formed at one sidethereof with a helicoidal reaction surface of zero transverse curvaturemaking a sli ht an 12 with the axial line of the thread for wet ging ofanother thread thereon, and with a helicoidal reaction surface disposedabruptly relatively to the axialline of the thread for limiting thewedging movement of a thread on said first-mentioned surface.

21. A tight-holding screw element having a screw thread one side ofwhich has a helicoidal reaction surface portion sloping transverselythereof toward the axial line of the thread within the angle of frictionto form a thread-binding surface, and also has a helicoidal reactionsurface portion disposed abruptly transveisely thereof to the axial lineof the thread and forming a binding action limiting abutment adjacentone edge of the first-mentioned reaction surface portion.

In testimony whereof I have signed this specification.

HUGUES LOUIS DARDELET.

